New Generalized Fatigue Model: Case of a Semi-elliptical Defect

A new fatigue crack model is proposed for long cracks, by generalization of Murakami's model established only for short cracks.The new model is based on the calculation of stress intensity factor (SIF), using directly the new areas created during the crack propagation with an efficiency that we consider acceptable. To take into account the behaviour of long cracks during propagation, a correction parameter denoted by was introduced. This parameter takes into account both the effect of the closure and the load ratio.The validation of the new model was realized using the fatigue crack growth data obtained by Boukharouba, on thick plates containing semi-elliptical defects in three-point bending, for three load ratios (R = 0.1, 0.3 and 0.5). One of advantages of the proposed new model is the computation of the SIF range () for all the crack front, not only two points, one at the surface and the second in the depth position, as it is to use. In this case, the evaluation of the crack closure effect becomes more realistic.We believe that the transition, during the fatigue crack propagation, from the plane stress to plane strain or vice versa, leads to an ambiguity in understanding this phenomenon. Support of both states simultaneously, plane strain and plane stress, by the proposed model represents the realistic solution to illustrate the influence of load ratio on the crack, especially for semi-elliptical and semi-circular cracks.